arXiv 1005.03382010-05-03astro-ph.CO

中性氢晕的共振散射和Ly-alpha辐射

Resonant Scattering and Ly-alpha Radiation Emergent from Neutral Hydrogen Halos

Ishani Roy, Chi-Wang Shu, Li-Zhi Fang

备注：: 25 pages, 10 figures, accepted for publication in ApJ
DOI：: 10.1088/0004-637X/716/1/604

摘要：

利用一种求解辐射转移积分-微分方程的数值方法，研究了Ly $α$光子$ν_0$从含有中心光源的光学厚晕中出射的通量.我们的重点是时间依赖的共振散射的影响。我们首先表明，在晕中的光子的频率分布迅速接近共振频率周围的局部热化状态，即使当辐射的平均强度是高度依赖于时间。由于初始条件在热化过程中被遗忘，如果出射光子主要来自热化态光子，则通量的某些特征，如其轮廓的双峰结构，实际上与中心源的本征宽度和时间行为无关。在这种情况下，差$|ν_{\pm}-ν_0|$（其中$ν_{\pm}$是通量的两个峰值的频率）不能小于多普勒展宽的$2$倍。然后，我们研究了中心源发射的光是闪光的情况下的辐射转移。我们计算了来自晕的通量的光变曲线。它表明通量仍然是一个闪光。然而，通量的闪光持续时间与光源的原始持续时间无关，而是取决于光晕的光学深度。因此，共振光子的空间转移是一个扩散过程，即使它不是纯粹的布朗扩散。这种性质使得光学厚晕能够在中心源发射停止后很长一段时间内在$ν_0$周围捕获和存储热化光子。被捕获在晕中的光子可以产生延迟辐射，其谱线也呈现出与局部热化光子谱线相同的双峰结构。讨论了这些结果的可能应用。

英文摘要：

With a state-of-the-art numerical method for solving the integral-differential equation of radiative transfer, we investigate the flux of the Ly$α$ photon $ν_0$ emergent from an optically thick halo containing a central light source. Our focus is on the time-dependent effects of the resonant scattering. We first show that the frequency distribution of photons in the halo are quickly approaching to a locally thermalized state around the resonant frequency, even when the mean intensity of the radiation is highly time-dependent. Since initial conditions are forgotten during the thermalization, some features of the flux, such as the two peak structure of its profile, actually are independent of the intrinsic width and time behavior of the central source, if the emergent photons are mainly from photons in the thermalized state. In this case, the difference $|ν_{\pm}-ν_0|$, where $ν_{\pm}$ are the frequencies of the two peaks of the flux, cannot be less than $2$ times of Doppler broadening. We then study the radiative transfer in the case where the light emitted from the central source is a flash. We calculate the light curves of the flux from the halo. It shows that the flux is still a flash. The time duration of the flash for the flux, however, is independent of the original time duration of the light source but depends on the optical depth of the halo. Therefore, the spatial transfer of resonant photons is a diffusion process, even though it is not a purely Brownian diffusion. This property enables an optically thick halo to trap and store thermalized photons around $ν_0$ for a long time after the cease of the central source emission. The photons trapped in the halo can yield delayed emission, of which the profile also shows typical two peak structure as that from locally thermalized photons. Possible applications of these results are addressed.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

摘要：

英文摘要：

相关论文